to the united nations, susan rice comes under fire again. this time, it's over rwanda. let's go "outfront. >>> good evening, welcome, everyone. "outfront" tonight breaking news, president obama puts the syrian president on notice. the president is reacting to new evidence that assad's regime has started mixing chemicals to make deadly sarin gas, adding to its massive stockpile of chemical weapons. >> and today i want to make it absolutely clear to assad and those under his command, the world is watching. the use of chemical weapons is and would be totally unacceptable. and if you make the tragic mistake of using these weapons, there will be consequences and you will be held accountable. >> assad is on the edge of president obama's so-called red line against syria. the president said this summer that syria's use or movement of chemical weapons could mean u.s. intervention. so outfront tonight, barbara star. how exactly -- how clear is the evidence that they are moving in a new step with chemical weapons. >> it was just over the weekend in the last few days the intelligence began coming in.